Conventionally, a method for producing cyclopentanone-2,3,5-tricarboxylic acid triester, which is comprised of allowing dimethyl itaconate to react with sodium salt of dimethyl malonate that is prepared from sodium hydride and dimethyl malonate, isolating a product (tetramethyl 1,1,3,4-butanetetracarboxylate) from resulting reaction mixture by purification with distillation after neutralizing with an acid, and then cyclizing the product in the presence of not less than one equivalent of sodium methoxide, and isolating a target compound from resultant reaction mixture after neutralizing with an acid, has been known (see U.S. Pat. No. 4,272,437, columns 361-362).
The above-mentioned conventional process requires twice neutralization treatment including that after the cyclization step, further purification with distillation, and the like, because of isolating a reaction product of dimethyl itaconate and sodium salt of dimethyl malonate once. These make steps very vexatious and complicated. Moreover, 1.07 molar equivalents of sodium methoxide is used as a base in the cyclization step, thereby the waste discharged from the neutralization treatment necessarily increases leading to a heavy load to the environment. Furthermore, yield of a cyclopentanone-2,3,5-tricarboxylic acid trimethylester is as low as 50% based on dimethylitaconate. Consequently, these problems make the conventional process unsuited to industrial applications, and the process has a room to be improved.
Accordingly, an object of the present invention is to provide a process that allows the industrially advantageous production of a cyclopentanone-2,3,5-tricarboxylic acid triester with a simple and convenient after-treatment and less waste.
The present inventors have diligently researched in order to solve the problems of the conventional process, and discovered as a result that by allowing an itaconic acid diester to react with a metal salt of malonic acid diester, and allowing obtained reaction mixture to react with an alcohol or a metal alkoxide, or a mixture-thereof, conversion to the desired cyclopentanone-2,3,5-tricarboxylic acid triester is enabled without isolating an adduct of an itaconic acid diester and a metal salt of malonic acid diester, or the adduct with neutralized form, which are intermediates, and accomplished the present invention.